Tony Blair never had the happiest of relationships with the trade unions. "When I addressed the TUC they were polite, but not much more than that," he wrote in his memoir, A Journey. "We both knew what we thought of each other … They couldn't understand why I was doing what I was doing; and I couldn't understand why they couldn't see it was the way of the future."

His successor but one, however, is a self-confessed admirer of the trade unions, without whose support he would not have been elected as Labour leader a year ago. Ed Miliband spent much time and effort wooing union bosses and activists: as James Macintyre and I reveal in our biography of him, in the run-up to the crucial vote by the Unite union's national policy committee in July 2010, Miliband rang several undecideds on the committee to personally persuade them to endorse him (having obtained their phone numbers from a friendly source inside Unite).

But there was no politeness from the unions on Tuesday when Miliband was heckled and jeered as he delivered his first speech to the TUC. It was a largely conciliatory address – except for his needlessly provocative condemnation of the one-day strike over pay and pensions by teachers and civil servants on 30 June. "While negotiations were going on, I do believe it was a mistake for strikes to happen," he said, to cries of "shame" from the audience. "I continue to believe that."

Ouch. It perhaps wasn't what he was expecting. "It doesn't do Ed any harm with the general public to be heckled at the TUC," a shadow cabinet minister tells me, "but that wasn't the purpose of the speech." The purpose, it seems, was to reach out to a disgruntled union movement, for whom Miliband has genuine affection, while restating his now familiar line: it is wrong to strike in the midst of ongoing talks with the government.

The argument may sound reasonable but it doesn't stand up to close examination. As TUC general secretary Brendan Barber pointed out: "Meaningful negotiations require two willing partners." Yet Treasury ministers switched the indexing of public sector pensions from Retail Price Index to the Consumer Price Index last year, without any consultation, wiping 15% off the value of the pension of every public sector worker. And, as Miliband admitted at the TUC: "Even before John Hutton's report was complete, they announced a 3% surcharge on millions of your members."

Why then has he set himself so resolutely against industrial action? When the unions go on strike on 30 November, does he realise he will find himself on the side not of teachers and nurses but David Cameron, George Osborne and Danny Alexander? And what is his answer to the question posed by Unison leader Dave Prentis: "Are we supposed to sit back, say it's unfair and do nothing?"

British politicians have a curious habit: they pay lip-service to the right to strike but tend never to back actual strikes (unless those strikes are overseas). "Are strikes only good enough for Tunisians and Egyptians?" asks a senior union leader. "Or Poles living under communism?" Union-bashing tends to be a popular pastime among the denizens of Westminster and the members of the commentariat. Meanwhile, "militant" trade union leaders are accused of "holding the country to ransom" – a charge that would be better applied to Barclays' Bob Diamond.

Friends of the Labour leader say he can't afford to be seen "in hock" to the unions or in open support of industrial action. The conventional wisdom says strikes are universally unpopular. As is so often the case, the conventional wisdom is wrong. Despite being fed a near-daily diet of anti-union propaganda by the media, the public isn't as hostile to strikes as some might assume.

Take the findings of two opinion polls conducted ahead of the one-day strike in June. Asked by ComRes if public sector workers pensions had "a legitimate reason to go on strike" over their pensions, 49% of the public agreed and just 35% disagreed. Meanwhile, Ipsos-Mori asked voters if they backed industrial action by public sector workers over jobs, pay and pensions, and found public opinion evenly split: 48% in support, 48% against. Polls also show that union officials are far more trusted than business leaders, journalists and politicians.

But Miliband is urged to keep his distance from the dastardly unions. "What I think is happening at the moment is that the leadership of the Labour party has got itself into a position where in order to pacify the voracious animal that is the rightwing press, or the undead Blairites, it is having this virility contest with the trade unions," Unite boss Len McCluskey told me. "I wish it wouldn't do that; I wish Ed wouldn't do that."

Now is not the time for posturing. The cuts are beginning to bite – and depressing report from the ONS revealed that unemployment grew by 80,000 during the three months to July, taking the total number of jobless to 2.5 million. The number of people employed in the public sector dropped by 111,000 in the three months to June – the biggest fall since records began in 1999. And the private sector created just one job for every 2.7 jobs lost in the public sector.

The unions' dire predictions have come to pass. The spectre of a double-dip recession looms. The chancellor, with his refusal to budge on spending cuts and his blind belief in a fictional "private sector-led recovery", is driving the UK economy off a cliff. So now is not the time for Miliband to be "picking a fight" or even "distancing" himself from the trade unions; now is the moment to be joining with them to create a national movement of opposition to, and resistance against, the coalition's fiscal barbarism.

We urgently need a more radical and stimulative alternative to cuts. That isn't just the opinion of trade union leaders but a view expressed by a growing number of "serious" opinion formers – from Nobel prize-winning economists like Paul Krugman and Joseph Stiglitz to the FT columnist Martin Wolf. Even Bill Gross, manager of the world's largest bond fund, Pimco, and a former Osborne ally, now says the coalition's austerity measures need "fine-tuning and perhaps re-routing".

A Japanese-style lost decade beckons. If Miliband and the Labour party cannot win the argument against austerity in parliament then the seven million-strong union movement – the country's biggest collection of voluntary organisations – will have to act as our last line of defence.